Theresa May is urged to call a fresh Brexit referendum by the former head of the UK civil service.

"A combination of poor negotiations and poor choices have left us in an unenviable place, and that's why we've got to re-open this question, even at this late stage," Lord Kerslake, who led the civil service between 2012 and 2014, tells BI.

Kerslake said the option of a no-deal Brexit should be taken off the ballot paper in a second vote, because "pursuing a no-deal Brexit [...] when you know the damage it could do to ordinary people is frankly irresponsible."

Downing Street has repeatedly ruled out the prospect of a second referendum.

LONDON — Theresa May should call a second Brexit referendum to avoid the potential "catastrophe" of a no-deal Brexit, the former head of the UK civil service has told Business Insider.

Lord Kerslake, who led the civil service between 2012 and 2014 and now advises Labour leader Jeremy Corbyn, told BI that the UK should be offered a two-choice referendum which includes the option to remain.

"I've changed my view and now back a second referendum," he told BI.

He explained that "a combination of poor negotiations and poor choices have left us in an unenviable place, and that's why we've got to re-open this question, even at this late stage."

Kerslake added that "no one could have imagined" the public would be facing the "stark choice between a poor deal or the catastrophe of no deal."

"Had the negotiating process gone better, we wouldn't be having this debate. It's possible the government will get a deal and be able to secure support for it in parliament, but that's looking pretty difficult to achieve now, as some very intractable issues like the Irish border have not been resolved."

But anti-Brexit campaigners who support a so-called "People's Vote" believe that the prime minister could be forced to legislate for such a scenario if MPs reject her deal in parliament.

Kerslake said the government should consider seeking an extension of Article 50 — the two-year EU exit process which will see the UK leave the EU in March next year — by several months to provide time for a second referendum.

"Pushing back the exit date is something that must now seriously be considered," he said. "If the government is unable to produce a deal and secure the vote in parliament, we are definitely into extension territory."

In another development, senior EU sources have also told Business Insider that they now believe the prospect of a second Brexit referendum is becoming increasingly likely.

"We were initially sceptical of [the possibility of a referendum] but it's looking much more likely than ever before," an EU Commission source told BI.

"If the meaningful vote fails in parliament then we believe the option of a second vote could come into play."

No-deal would be a 'catastrophe'

Kerslake told BI that May's government should remove the option of a "no-deal" scenario from the ballot paper, and offer voters a simple choice between remaining in the EU and accepting the terms of Theresa May's Brexit deal.

He said that a no-deal Brexit was "not tenable" because it would wreak havoc on the economy and because the civil service was unable to prepare for such a radical change in policy at short notice.

"Pursuing a no-deal Brexit, or even contemplating it when you know the damage it could do to ordinary people is frankly irresponsible," he said.

"We shouldn't really consider it as an option, because its consequences are so enormous," he said. "The economic shock would be very significant."

He branded trade secretary Liam Fox "irresponsible" for suggesting that leaving the EU would not have a significant economic impact, and criticised Tory MP Jacob Rees-Mogg, who has repeatedly called for the UK to leave without a deal.

"Those people who are saying "Let's not worry about it, let's crash out of the EU, it'll be much easier than you think," are people of means on the whole," he said.

"Jacob Rees-Mogg is not going to be proved wrong on this point. But the vast bulk of the British population are living much closer to the edge than people like that. They cannot withstand an economic shock without real consequences to them."

"More and more people are realising, when faced with the miserable deal on offer, that a People's Vote is the way out of the Brexit mess. The Government cannot get us a good deal and there is no majority in Westminster for any of the Brexit options and so it must be for the people to have the final say on a decision of this importance."